package main import ( "fmt" "github.com/btcsuite/btcd/txscript" "github.com/btcsuite/btcd/wire" "github.com/btcsuite/btcutil" "github.com/davecgh/go-spew/spew" "github.com/lightningnetwork/lnd/htlcswitch" "github.com/lightningnetwork/lnd/lnwallet" "github.com/lightningnetwork/lnd/lnwire" ) var ( // ErrChanAlreadyClosing is returned when a channel shutdown is // attempted more than once. ErrChanAlreadyClosing = fmt.Errorf("channel shutdown already initiated") // ErrChanCloseNotFinished is returned when a caller attempts to access // a field or function that is contingent on the channel closure // negotiation already being completed. ErrChanCloseNotFinished = fmt.Errorf("close negotiation not finished") // ErrInvalidState is returned when the closing state machine receives // a message while it is in an unknown state. ErrInvalidState = fmt.Errorf("invalid state") ) // closeState represents all the possible states the channel closer state // machine can be in. Each message will either advance to the next state, or // remain at the current state. Once the state machine reaches a state of // closeFinished, then negotiation is over. type closeState uint8 const ( // closeIdle is the initial starting state. In this state, the state // machine has been instantiated, but no state transitions have been // attempted. If a state machine receives a message while in this // state, then it is the responder to an initiated cooperative channel // closure. closeIdle closeState = iota // closeShutdownInitiated is the state that's transitioned to once the // initiator of a closing workflow sends the shutdown message. At this // point, they're waiting for the remote party to respond with their // own shutdown message. After which, they'll both enter the fee // negotiation phase. closeShutdownInitiated // closeFeeNegotiation is the third, and most persistent state. Both // parties enter this state after they've sent and received a shutdown // message. During this phase, both sides will send monotonically // increasing fee requests until one side accepts the last fee rate // offered by the other party. In this case, the party will broadcast // the closing transaction, and send the accepted fee to the remote // party. This then causes a shift into the closeFinished state. closeFeeNegotiation // closeFinished is the final state of the state machine. In this, // state a side has accepted a fee offer and has broadcast the valid // closing transaction to the network. During this phase, the closing // transaction becomes available for examination. closeFinished ) // chanCloseCfg holds all the items that a channelCloser requires to carry out // its duties. type chanCloseCfg struct { // channel is the channel that should be closed. channel *lnwallet.LightningChannel // unregisterChannel is a function closure that allows the // channelCloser to re-register a channel. Once this has been done, no // further HTLC's should be routed through the channel. unregisterChannel func(lnwire.ChannelID) // broadcastTx broadcasts the passed transaction to the network. broadcastTx func(*wire.MsgTx) error // disableChannel disables a channel, resulting in it not being able to // forward payments. disableChannel func(wire.OutPoint) error // quit is a channel that should be sent upon in the occasion the state // machine should cease all progress and shutdown. quit chan struct{} } // channelCloser is a state machine that handles the cooperative channel // closure procedure. This includes shutting down a channel, marking it // ineligible for routing HTLC's, negotiating fees with the remote party, and // finally broadcasting the fully signed closure transaction to the network. type channelCloser struct { // state is the current state of the state machine. state closeState // cfg holds the configuration for this channelCloser instance. cfg chanCloseCfg // chanPoint is the full channel point of the target channel. chanPoint wire.OutPoint // cid is the full channel ID of the target channel. cid lnwire.ChannelID // negotiationHeight is the height that the fee negotiation begun at. negotiationHeight uint32 // closingTx is the final, fully signed closing transaction. This will // only be populated once the state machine shifts to the closeFinished // state. closingTx *wire.MsgTx // idealFeeSat is the ideal fee that the state machine should initially // offer when starting negotiation. This will be used as a baseline. idealFeeSat btcutil.Amount // lastFeeProposal is the last fee that we proposed to the remote // party. We'll use this as a pivot point to rachet our next offer up, // or down, or simply accept the remote party's prior offer. lastFeeProposal btcutil.Amount // priorFeeOffers is a map that keeps track of all the proposed fees // that we've offered during the fee negotiation. We use this map to // cut the negotiation early if the remote party ever sends an offer // that we've sent in the past. Once negotiation terminates, we can // extract the prior signature of our accepted offer from this map. // // TODO(roasbeef): need to ensure if they broadcast w/ any of our prior // sigs, we are aware of priorFeeOffers map[btcutil.Amount]*lnwire.ClosingSigned // closeReq is the initial closing request. This will only be populated // if we're the initiator of this closing negotiation. // // TODO(roasbeef): abstract away closeReq *htlcswitch.ChanClose // localDeliveryScript is the script that we'll send our settled // channel funds to. localDeliveryScript []byte // remoteDeliveryScript is the script that we'll send the remote // party's settled channel funds to. remoteDeliveryScript []byte } // newChannelCloser creates a new instance of the channel closure given the // passed configuration, and delivery+fee preference. The final argument should // only be populated iff, we're the initiator of this closing request. func newChannelCloser(cfg chanCloseCfg, deliveryScript []byte, idealFeePerKw lnwallet.SatPerKWeight, negotiationHeight uint32, closeReq *htlcswitch.ChanClose) *channelCloser { // Given the target fee-per-kw, we'll compute what our ideal _total_ // fee will be starting at for this fee negotiation. // // TODO(roasbeef): should factor in minimal commit idealFeeSat := cfg.channel.CalcFee(idealFeePerKw) // If this fee is greater than the fee currently present within the // commitment transaction, then we'll clamp it down to be within the // proper range. // // TODO(roasbeef): clamp fee func? channelCommitFee := cfg.channel.StateSnapshot().CommitFee if idealFeeSat > channelCommitFee { peerLog.Infof("Ideal starting fee of %v is greater than "+ "commit fee of %v, clamping", int64(idealFeeSat), int64(channelCommitFee)) idealFeeSat = channelCommitFee } peerLog.Infof("Ideal fee for closure of ChannelPoint(%v) is: %v sat", cfg.channel.ChannelPoint(), int64(idealFeeSat)) cid := lnwire.NewChanIDFromOutPoint(cfg.channel.ChannelPoint()) return &channelCloser{ closeReq: closeReq, state: closeIdle, chanPoint: *cfg.channel.ChannelPoint(), cid: cid, cfg: cfg, negotiationHeight: negotiationHeight, idealFeeSat: idealFeeSat, localDeliveryScript: deliveryScript, priorFeeOffers: make(map[btcutil.Amount]*lnwire.ClosingSigned), } } // initChanShutdown begins the shutdown process by un-registering the channel, // and creating a valid shutdown message to our target delivery address. func (c *channelCloser) initChanShutdown() (*lnwire.Shutdown, error) { // With both items constructed we'll now send the shutdown message for // this particular channel, advertising a shutdown request to our // desired closing script. shutdown := lnwire.NewShutdown(c.cid, c.localDeliveryScript) // TODO(roasbeef): err if channel has htlc's? // Before returning the shutdown message, we'll unregister the channel // to ensure that it isn't seen as usable within the system. // // TODO(roasbeef): fail if err? c.cfg.unregisterChannel(c.cid) peerLog.Infof("ChannelPoint(%v): sending shutdown message", c.chanPoint) return shutdown, nil } // ShutdownChan is the first method that's to be called by the initiator of the // cooperative channel closure. This message returns the shutdown message to // send to the remote party. Upon completion, we enter the // closeShutdownInitiated phase as we await a response. func (c *channelCloser) ShutdownChan() (*lnwire.Shutdown, error) { // If we attempt to shutdown the channel for the first time, and we're // not in the closeIdle state, then the caller made an error. if c.state != closeIdle { return nil, ErrChanAlreadyClosing } peerLog.Infof("ChannelPoint(%v): initiating shutdown of", c.chanPoint) shutdownMsg, err := c.initChanShutdown() if err != nil { return nil, err } // With the opening steps complete, we'll transition into the // closeShutdownInitiated state. In this state, we'll wait until the // other party sends their version of the shutdown message. c.state = closeShutdownInitiated // Finally, we'll return the shutdown message to the caller so it can // send it to the remote peer. return shutdownMsg, nil } // ClosingTx returns the fully signed, final closing transaction. // // NOTE: This transaction is only available if the state machine is in the // closeFinished state. func (c *channelCloser) ClosingTx() (*wire.MsgTx, error) { // If the state machine hasn't finished closing the channel then we'll // return an error as we haven't yet computed the closing tx. if c.state != closeFinished { return nil, ErrChanCloseNotFinished } return c.closingTx, nil } // CloseRequest returns the original close request that prompted the creation // of the state machine. // // NOTE: This will only return a non-nil pointer if we were the initiator of // the cooperative closure workflow. func (c *channelCloser) CloseRequest() *htlcswitch.ChanClose { return c.closeReq } // ProcessCloseMsg attempts to process the next message in the closing series. // This method will update the state accordingly and return two primary values: // the next set of messages to be sent, and a bool indicating if the fee // negotiation process has completed. If the second value is true, then this // means the channelCloser can be garbage collected. func (c *channelCloser) ProcessCloseMsg(msg lnwire.Message) ([]lnwire.Message, bool, error) { switch c.state { // If we're in the close idle state, and we're receiving a channel // closure related message, then this indicates that we're on the // receiving side of an initiated channel closure. case closeIdle: // First, we'll assert that we have a channel shutdown message, // otherwise, this is an attempted invalid state transition. shutDownMsg, ok := msg.(*lnwire.Shutdown) if !ok { return nil, false, fmt.Errorf("expected lnwire.Shutdown, "+ "instead have %v", spew.Sdump(msg)) } // Next, we'll note the other party's preference for their // delivery address. We'll use this when we craft the closure // transaction. c.remoteDeliveryScript = shutDownMsg.Address // We'll generate a shutdown message of our own to send across // the wire. localShutdown, err := c.initChanShutdown() if err != nil { return nil, false, err } peerLog.Infof("ChannelPoint(%v): Responding to shutdown", c.chanPoint) msgsToSend := make([]lnwire.Message, 0, 2) msgsToSend = append(msgsToSend, localShutdown) // After the other party receives this message, we'll actually // start the final stage of the closure process: fee // negotiation. So we'll update our internal state to reflect // this, so we can handle the next message sent. c.state = closeFeeNegotiation // We'll also craft our initial close proposal in order to keep // the negotiation moving, but only if we're the negotiator. if c.cfg.channel.IsInitiator() { closeSigned, err := c.proposeCloseSigned(c.idealFeeSat) if err != nil { return nil, false, err } msgsToSend = append(msgsToSend, closeSigned) } // We'll return both sets of messages to send to the remote // party to kick off the fee negotiation process. return msgsToSend, false, nil // If we just initiated a channel shutdown, and we receive a new // message, then this indicates the other party is ready to shutdown as // well. In this state we'll send our first signature. case closeShutdownInitiated: // First, we'll assert that we have a channel shutdown message, // otherwise, this is an attempted invalid state transition. shutDownMsg, ok := msg.(*lnwire.Shutdown) if !ok { return nil, false, fmt.Errorf("expected lnwire.Shutdown, "+ "instead have %v", spew.Sdump(msg)) } // Now that we know this is a valid shutdown message, we'll // record their preferred delivery closing script. c.remoteDeliveryScript = shutDownMsg.Address // At this point, we can now start the fee negotiation state, // by constructing and sending our initial signature for what // we think the closing transaction should look like. c.state = closeFeeNegotiation peerLog.Infof("ChannelPoint(%v): shutdown response received, "+ "entering fee negotiation", c.chanPoint) // Starting with our ideal fee rate, we'll create an initial // closing proposal, but only if we're the initiator, as // otherwise, the other party will send their first proposal // first. if c.cfg.channel.IsInitiator() { closeSigned, err := c.proposeCloseSigned(c.idealFeeSat) if err != nil { return nil, false, err } return []lnwire.Message{closeSigned}, false, nil } return nil, false, nil // If we're receiving a message while we're in the fee negotiation // phase, then this indicates the remote party is responding to a closed // signed message we sent, or kicking off the process with their own. case closeFeeNegotiation: // First, we'll assert that we're actually getting a // CloseSigned message, otherwise an invalid state transition // was attempted. closeSignedMsg, ok := msg.(*lnwire.ClosingSigned) if !ok { return nil, false, fmt.Errorf("expected lnwire.ClosingSigned, "+ "instead have %v", spew.Sdump(msg)) } // We'll compare the proposed total fee, to what we've proposed // during the negotiations, if it doesn't match any of our // prior offers, then we'll attempt to rachet the fee closer to remoteProposedFee := closeSignedMsg.FeeSatoshis if _, ok := c.priorFeeOffers[remoteProposedFee]; !ok { // We'll now attempt to rachet towards a fee deemed // acceptable by both parties, factoring in our ideal // fee rate, and the last proposed fee by both sides. feeProposal := calcCompromiseFee(c.chanPoint, c.idealFeeSat, c.lastFeeProposal, remoteProposedFee, ) // With our new fee proposal calculated, we'll craft a // new close signed signature to send to the other // party so we can continue the fee negotiation // process. closeSigned, err := c.proposeCloseSigned(feeProposal) if err != nil { return nil, false, err } // If the compromise fee doesn't match what the peer // proposed, then we'll return this latest close signed // message so we continue negotiation. if feeProposal != remoteProposedFee { peerLog.Debugf("ChannelPoint(%v): close tx "+ "fee disagreement, continuing negotiation", c.chanPoint) return []lnwire.Message{closeSigned}, false, nil } } peerLog.Infof("ChannelPoint(%v) fee of %v accepted, ending "+ "negotiation", c.chanPoint, remoteProposedFee) // Otherwise, we've agreed on a fee for the closing // transaction! We'll craft the final closing transaction so // we can broadcast it to the network. matchingSig := c.priorFeeOffers[remoteProposedFee].Signature localSigBytes := matchingSig.ToSignatureBytes() localSig := append(localSigBytes, byte(txscript.SigHashAll)) remoteSigBytes := closeSignedMsg.Signature.ToSignatureBytes() remoteSig := append(remoteSigBytes, byte(txscript.SigHashAll)) closeTx, _, err := c.cfg.channel.CompleteCooperativeClose( localSig, remoteSig, c.localDeliveryScript, c.remoteDeliveryScript, remoteProposedFee, ) if err != nil { return nil, false, err } c.closingTx = closeTx // Before closing, we'll attempt to send a disable update for // the channel. We do so before closing the channel as otherwise // the current edge policy won't be retrievable from the graph. if err := c.cfg.disableChannel(c.chanPoint); err != nil { peerLog.Warnf("Unable to disable channel %v on "+ "close: %v", c.chanPoint, err) } // With the closing transaction crafted, we'll now broadcast it // to the network. peerLog.Infof("Broadcasting cooperative close tx: %v", newLogClosure(func() string { return spew.Sdump(closeTx) })) if err := c.cfg.broadcastTx(closeTx); err != nil { return nil, false, err } if err := c.cfg.channel.MarkCommitmentBroadcasted(); err != nil { return nil, false, err } // Finally, we'll transition to the closeFinished state, and // also return the final close signed message we sent. // Additionally, we return true for the second argument to // indicate we're finished with the channel closing // negotiation. c.state = closeFinished matchingOffer := c.priorFeeOffers[remoteProposedFee] return []lnwire.Message{matchingOffer}, true, nil // If we receive a message while in the closeFinished state, then this // should only be the remote party echoing the last ClosingSigned // message that we agreed on. case closeFinished: if _, ok := msg.(*lnwire.ClosingSigned); !ok { return nil, false, fmt.Errorf("expected "+ "lnwire.ClosingSigned, instead have %v", spew.Sdump(msg)) } // There's no more to do as both sides should have already // broadcast the closing transaction at this state. return nil, true, nil // Otherwise, we're in an unknown state, and can't proceed. default: return nil, false, ErrInvalidState } } // proposeCloseSigned attempts to propose a new signature for the closing // transaction for a channel based on the prior fee negotiations and our // current compromise fee. func (c *channelCloser) proposeCloseSigned(fee btcutil.Amount) (*lnwire.ClosingSigned, error) { rawSig, _, _, err := c.cfg.channel.CreateCloseProposal( fee, c.localDeliveryScript, c.remoteDeliveryScript, ) if err != nil { return nil, err } // We'll note our last signature and proposed fee so when the remote // party responds we'll be able to decide if we've agreed on fees or // not. c.lastFeeProposal = fee parsedSig, err := lnwire.NewSigFromRawSignature(rawSig) if err != nil { return nil, err } peerLog.Infof("ChannelPoint(%v): proposing fee of %v sat to close "+ "chan", c.chanPoint, int64(fee)) // We'll assemble a ClosingSigned message using this information and // return it to the caller so we can kick off the final stage of the // channel closure project. closeSignedMsg := lnwire.NewClosingSigned(c.cid, fee, parsedSig) // We'll also save this close signed, in the case that the remote party // accepts our offer. This way, we don't have to re-sign. c.priorFeeOffers[fee] = closeSignedMsg return closeSignedMsg, nil } // feeInAcceptableRange returns true if the passed remote fee is deemed to be // in an "acceptable" range to our local fee. This is an attempt at a // compromise and to ensure that the fee negotiation has a stopping point. We // consider their fee acceptable if it's within 30% of our fee. func feeInAcceptableRange(localFee, remoteFee btcutil.Amount) bool { // If our offer is lower than theirs, then we'll accept their // offer if it's no more than 30% *greater* than our current // offer. if localFee < remoteFee { acceptableRange := localFee + ((localFee * 3) / 10) return remoteFee <= acceptableRange } // If our offer is greater than theirs, then we'll accept their offer // if it's no more than 30% *less* than our current offer. acceptableRange := localFee - ((localFee * 3) / 10) return remoteFee >= acceptableRange } // rachetFee is our step function used to inch our fee closer to something that // both sides can agree on. If up is true, then we'll attempt to increase our // offered fee. Otherwise, if up is false, then we'll attempt to decrease our // offered fee. func rachetFee(fee btcutil.Amount, up bool) btcutil.Amount { // If we need to rachet up, then we'll increase our fee by 10%. if up { return fee + ((fee * 1) / 10) } // Otherwise, we'll *decrease* our fee by 10%. return fee - ((fee * 1) / 10) } // calcCompromiseFee performs the current fee negotiation algorithm, taking // into consideration our ideal fee based on current fee environment, the fee // we last proposed (if any), and the fee proposed by the peer. func calcCompromiseFee(chanPoint wire.OutPoint, ourIdealFee, lastSentFee, remoteFee btcutil.Amount) btcutil.Amount { // TODO(roasbeef): take in number of rounds as well? peerLog.Infof("ChannelPoint(%v): computing fee compromise, ideal=%v, "+ "last_sent=%v, remote_offer=%v", chanPoint, int64(ourIdealFee), int64(lastSentFee), int64(remoteFee)) // Otherwise, we'll need to attempt to make a fee compromise if this is // the second round, and neither side has agreed on fees. switch { // If their proposed fee is identical to our ideal fee, then we'll go // with that as we can short circuit the fee negotiation. Similarly, if // we haven't sent an offer yet, we'll default to our ideal fee. case ourIdealFee == remoteFee || lastSentFee == 0: return ourIdealFee // If the last fee we sent, is equal to the fee the remote party is // offering, then we can simply return this fee as the negotiation is // over. case remoteFee == lastSentFee: return lastSentFee // If the fee the remote party is offering is less than the last one we // sent, then we'll need to rachet down in order to move our offer // closer to theirs. case remoteFee < lastSentFee: // If the fee is lower, but still acceptable, then we'll just // return this fee and end the negotiation. if feeInAcceptableRange(lastSentFee, remoteFee) { peerLog.Infof("ChannelPoint(%v): proposed remote fee "+ "is close enough, capitulating", chanPoint) return remoteFee } // Otherwise, we'll rachet the fee *down* using our current // algorithm. return rachetFee(lastSentFee, false) // If the fee the remote party is offering is greater than the last one // we sent, then we'll rachet up in order to ensure we terminate // eventually. case remoteFee > lastSentFee: // If the fee is greater, but still acceptable, then we'll just // return this fee in order to put an end to the negotiation. if feeInAcceptableRange(lastSentFee, remoteFee) { peerLog.Infof("ChannelPoint(%v): proposed remote fee "+ "is close enough, capitulating", chanPoint) return remoteFee } // Otherwise, we'll rachet the fee up using our current // algorithm. return rachetFee(lastSentFee, true) default: // TODO(roasbeef): fail if their fee isn't in expected range return remoteFee } }